U.S. Pat. No. 5,281,562 (Araujo et al.) is directed to the production of non-photochromic glasses containing a cuprous halide or a cuprous-cadmium halide crystal phase which exhibit a sharp spectral cutoff at a wavelength of about 400 nm, those glasses having base compositions consisting essentially, expressed in terms of cation percent on the oxide basis, of 35-73% SiO.sub.2, 15-45% B.sub.2 O.sub.3, 0-12% Al.sub.2 O.sub.3, the Al.sub.2 O.sub.3 being less than 10% when SiO.sub.2 is greater than 55%, 0-12% Li.sub.2 O, 0-20% Na.sub.2 O, 0-12% K.sub.2 O, 4.75-20% Li.sub.2 O+Na.sub.2 O+K.sub.2 O, 0-5% CaO and/or SrO and/or BaO, 0.125-1.0% Cu.sub.2 O, 0-1% CdO, 0-5% ZrO.sub.2, 0-0.75% SnO.sub.2, and 0-1% As.sub.2 O.sub.3 and/or Sb.sub.2 O.sub.3, and containing, expressed in terms of weight percent, 0-1.75% Cl, 0-1.0% Br, 0.25-2.0% Cl+Br, and 0-2% F, said glass having an R-value, calculated in terms of mole percent, of 0.15-0.45, the R-value not exceeding 0.30 except as the glass composition meets at least one condition selected from the group consisting of up to 12 cation % Li.sub.2 O, less than 10 cation % Al.sub.2 O.sub.3, at least 0.3 cation % Cu.sub.2 O, and 0.5-2.0 weight % Cl+Br.
The R-value is noted in the patent as constituting a measure of the basicity of a glass and as being defined by the formula ##EQU1## wherein M.sub.2 O represents alkali metal oxides and RO represents alkaline earth metal oxides.
Those glasses are transparent in the visible region of the radiation spectrum, but are essentially opaque to ultraviolet radiation; i.e., those glasses essentially completely block radiation in that region of the electromagnetic spectrum having wavelengths of 400 nm and shorter. Accordingly, those glasses can be utilized in laser shield applications involving radiation in the ultraviolet region of the spectrum. As utilized herein, the expressions "essentially completely" and "essentially opaque" mean that, whereas it is most preferred that all of the ultraviolet radiation will be blocked, it is possible that a small amount will be passed, but that amount is so small as to have a negligible effect upon the use of the glasses for laser protection.
U.S. Pat. No. 5,281,562 is expressly incorporated herein by reference.
Whereas the above-described glasses exhibit very effective spectral cutoffs of radiation having wavelengths of 400 nm and shorter, they were found to be unacceptable, however, when subjected to laser radiation having wavelengths between 400-550 nm.
Therefore, the principal objective of the present invention was to provide glass articles transparent in the visible region of the electromagnetic spectrum, but essentially opaque to radiation in the ultraviolet region of the spectrum and up to radiation having a wavelength of 550 nm.
A complementary objective was to devise a method for preparing such glass articles.
A specific objective was to devise glass compositions to be used in lenses to protect the eyeglass wearer from eye damage upon exposure to laser radiation.